1. Field of the Invention
The present invention generally relates to well equipment and more particularly to an improved sucker rod assembly.
2. Prior Art
Conventional sucker rods are usually fabricated of metal in lengths of about 25 to 40 feet. These lengths are interconnected to form sucker rod strings useful for well pumping purposes. Because metal sucker rod strings are relatively heavy, recently efforts have been made toward developing and using sucker rods which include non-metallic components. For example, U.S. Pat. No. 3,212,582 discloses the use of plastic sucker rods; so also does U.S. Pat. No. 3,889,579. U.S. Pat. Nos. 4,360,288; 4,401,396, 4,024,913 and 4,416,329 also disclose non-metallic sucker rods. Certain of such non-metallic sucker rods have been provided in continuous lengths. See for example U.S. Pat. Nos. 4,416,329 and 3,889,579.
Difficulties have been encountered with non-metallic sucker rods whether of the continuous type or of the multiple interconnected type. In this regard, non-metallic sucker rods such as those made of plastic, fiberglass or other non-metallic fibrous compositions are relatively difficult to grip with end fittings without having the end fittings slip off or crush the rod ends. Additionally, since the rods flex, some difficulties have been encountered with so-called pinch-off of the rods at about the point of exit of the rod from the end fitting.
Various patents have been addressed to the provision of improved designs of metallic fittings used on non-metallic sucker rod ends; see for example U.S. Pat. Nos. 4,360,288 and 4,401,396. Certain end fittings for non-metallic sucker rods have been provided which include a plurality of internal steps or teeth formed by pouring molten potting material into configured end fitting cavities. Specially configuring the casing can be expensive and the results are variable. The potting material is set to hardness and bonds to the sucker rod exterior. The set potting compound may or may not bond to the interior surface of the fitting. Loosening of that bond can occur due to the shape of the set potting material, with subsequent slipping of the fitting and potting material from the rod, resulting in loss of the rod, interruption of well pumping activity, etc.
Accordingly, there is a need for an improved sucker rod assembly which employs a non-metallic sucker rod held by improved rod end fittings. The end fittings should securely hold the rod ends without crushing or pinch-off for improved sucker rod longevity. The assembly should have improved load-bearing characteristics and efficiency.